Method of manufacturing finished welded tubing

ABSTRACT

Flat prefinished metal strip is continuously converted to prefinished tube in a tube forming and welding process which includes continuous application of a film matching strip to the tubing in the region of the weld while the tubing is still hot from the welding operation. The film strip includes a surface which is at least partially heat-fusible at the temperature of the tubing surface at the point at which the film strip is applied and is adherent thereto.

United States Patent Inventor John E. Masters Barrington, Ill.

App]. No. 825,287

Filed May 16, 1969 Patented Aug. 24, 1971 Assignee Pre Finkh Metak, Inc.

Elk Grove Village, lll.

METHOD OF MANUFACTURING FINISHED WELDED TUBING [56] References CitedUNlTED STATES PATENTS 3,332,138 7/1967 Gamer 29/430 3,394,450 7/1968Gill et al. .7 29/430 Primary ExaminerThomas H. Eager Attorney-Barbe,Robertson & Vandenburgh ABSTRACT: Flat prefinished metal strip iscontinuously con- 3C nnmwmgm verted to prefinished tube in a tubeforming and welding U.S.Cl.. 29/430, process which includes continuousapplication of a film 29/475 matching strip to the tubing in the regionof the weld while the Int. Cl ..B23 19/00, tubing is still hot from thewelding operation. The film strip in- B23k 31/02 cludes a surface whichis at least partially heat-fusible at the Field of Search 29/430,mperature of the tubing surface at the point at which the 200, 429, 417,475 film strip is applied and is adherent thereto.

TA PE 10 COOLA Mr A B 22 1d- 44 wfl 0 L6.- g j f yg 12 \7 TEMPERATUREZONE 600 -300 7 M iQi-l. 6-4

HOT ENOUGH I G/M nv 5/0: T0 PARTIALLY STR, j] I Mar TAPE T0 51 END WITHTUBE METHOD OF MANUFACTURING FINISHED WELDED TUBING BACKGROUND OF THEINVENTION Equipment and methods for converting continuous metal strip toround welded tube are well known. However, it is highly desirable toprovide metal tubing which is prefinished either in solid decorativecolors or with complex finishes such as those resembling wood grain.Such decorated tubing is useful in the fabrication of ironing boards,lawn equipment and the like. However, I know of no satisfactory way ofincorporating a complex finish such as a wood grain finish around theentire circumference of a metal tube. Moreover, conversion of aprefinished elongated metal strip into a welded tube in accordance withmethods heretofore available result in an unfinished weld line witheither bare metal or burnt plastic along the side thereof.

It is an object of this invention to provide an innovation which isreadily adaptable to conventional welded tube forming processes, whichinnovation results in a welded tube which is finished around the entirecircumference thereof. It is particularly an object of this invention toprovide a method of converting elongated flat metal strip into weldedtubing having a wood grain finish around the entire circumferencethereof.

SUMMARY OF THE INVENTION In accordance with this invention, elongatedprefinished metal strip is continuously converted to prefinished weldedtube. The prefinished metal strip is formed into a tube and welded inaccordance with conventional technology. However, immediately after theedges are welded together and while the weld line and the regionimmediately adjacent thereto are still hot as a result of the weldingstep, and organic film which matches the finish of the metal strip andhas one surface which is at least partially fusible at temperaturesbetween 300 and 600 Fahrenheit is applied to the welded tubing at apoint at which the welded tubing is cool enough to be tolerated by theorganic strip, and yet high enough to at least partially fuse thecontacting surface to cause the film to adhere to the tubing.

DESIGNATION OF THE FIGURES OF THE DRAWING FIG. 1 is a schematic viewillustrating the various stages or steps of the overall method startingwith elongated metal strip and ending with completely finished weldedtube.

FIG. 2 is a perspective view showing a portion of the elongated metalstrip which is converted to welded tube in accordance with thisinvention.

FIG. 3 is an enlarged perspective view illustrating the conventionalforming step in which the elongated metal strip is shaped to tubeconfiguration.

FIG. 4, is a schematic cross-sectional perspective view of a portion ofthe continuous worked metal as viewed approximately along the line 4-4of FIG. 1.

FIG. 5 is also a perspective schematic cross-sectional view of a portionof the continuous worked material as is viewed approximately along theline 5-5 of FIG. 1.

FIG. 6 is a schematic perspective cross-sectional view takenapproximately along the line 6-6 of FIG. 1.

FIG. 7 is a greatly enlarged cross-sectional view of a small portion ofa cross section taken approximately along the line 7-7 of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS Although the following disclosureoffered for public dissemination, in return for the grant of a patent,is detailed to ensure adequacy and aid understanding, this is notintended to prejudice that purpose of a patent which is to cover eachnew inventive concept therein no matter how others may later disguise itby variations in form or additions or further improvements. The claimsat the end hereof are intended as the chief aid toward this purpose; asit is these that meet the requirement of pointing out the parts,improvements, or combinations in which the inventive concepts are found.

In accordance with this invention flat prefinished strip, generally 10,is shaped to generate a substantially circular cross section wherebyopposing edges 11, 11' are brought into abutting relation andcontinuously welded together. Inasmuch as apparatus is well known foraccomplishing the forming and welding step it is not shown on theaccompanying drawings. In conventional methods the tube may be scarfedor scraped immediately prior to the welding operation in order to removemetal oxide and provide smooth surface for the welding operation. Inaccomplishing these conventional steps the flat metal strip is usuallyfed continuously into the forming and welding equipment at a relativelyhigh speed, for example, 200 feet per minute. The temperatures of themetal at the point of weld are very high, e.g., 2000 Fahrenheit and thistemperature is conventionally brought down suddenly through the use ofcoolant liquids, e.g., oil, which is brought into the interior 15 of thenewly formed welded tube by means of a conduit 15. Thus, conduit 15 ismaintained fixed with respect to the forming and welding equipmentalthough the newly formed tube moves at a high rate with respect to it.In FIG. 1, Zone A illustrates the region in which the welding occurs,and Zone B, the region of coolant injection. Hence coolant is injectedinto the interior 15 immediately beyond or downstream from the weld ZoneA. Thus, some of the heat of the weld line 17 is removed from the weldedtube 12 by coolant, and some is carried circumferentially through metaltube wall 19. Thus as the newly formed tube travels along at high speed,e.g. 200 feet per minute, the temperature at any one point is more orless constant, there being a rapidly falling gradient beginning at thepoint at which coolant is injected. Thus, as the newly formed tubetravels through the equipment it passes through a zone in which theimmediate region of the weld line 17 has surface temperatures in therange 300 to 600 Fahrenheit and this zone is fixed, for a given set ofoperating conditions, with respect to the forming and welding equipment.

In accordance with this invention a special tape 22, i.e., one whichmatches in appearance the finish of the metal strip, is applied to theheated region in that zone in which the temperature is 300 to 600Fahrenheit. The special tape which is used in accordance with thisinvention is at least one-half mil and preferably less than two mils inthickness. Tapes which are less than one-half mil in thickness generallydo not have sufficient strength for use in accordance with thisinvention. Tapes substantially in excess of two mil thickness arewasteful of material, and moreover provide edges thereof which are toothick to be readily concealed.

In accordance with a preferred embodiment of this invention in which awood grain finished tubing is prepared, the metal strip is provided witha wood grain finish and the tape comprises a laminate plastic film 25,which is substantially transparent, having matching wood grain printing26 on one side thereof and also includes a layer 27 of high meltadhesive on the printed side of the tape.

The preferred tape is thus applied by any conventional equipment forapplying tape, e.g. under a compression roller to the heated region ofthe tubing in which the temperature is in the 300 to 600 range. Thus,the high melt adhesive used on the special tape must be one of theconventional high melt adhesives which is activated by temperatures inthe 300 to 600 range. The adhesive layer 27 is thus partially fusedthereby integrating the tape 22 and the heated surface of wall 19 afterthe temperatures fall below the solidification temperatures of theparticular adhesive.

Conventionally tubing formed by the continuous butt welding equipment iscut into standardized lengths shortly after the tubing is formed. Thecoolant is discharged from the segments of finished, cut, butt-weldedtubing, and is filtered and recirculated. I have found that the plasticfilm, or tape which is used in accordance with this invention has to beable to stand temperatures of 300 to 600 Fahrenheit for at least a shortperiod of time, must be scuff resistant, and of relatively high tensilestrength in order to endure subsequent fabrication, e.g. conversion oftubing into ironing board legs, lawn equipment, etc. I have found thatpolypropylene and high density polyethylene are not suitable for use asplastic film in accordance with this invention because they respond toodrastically to the high temperatures involved in the method of thisinvention. I have found Mylar (DuPont trademark) and other terphthalicesters, Korad (Rohm and Haas trademark) and other acrylic tape polymers,Tedlar (DuPont trademark) and other polyvinyl fluoride films, Videne(Goodyear Chemical Co. trademark) and other polyesters are satisfactoryas plastic film for use in accordance with this invention. It ispreferred that the tape be subjected to compression, e.g. by siliconerubber nip-type roller, immediately upon contact with the heatedsurface.

' While the embodiments of apparatus and method of this inventiondescribed above illustrate application to round tubing, the invention isalso useful with square, rectangular and odd shaped tubes as well.

If the finish to be applied is a solid color finish the tape which isapplied in accordance with this invention may be colored throughoutrather than reverse printed, providing at least one surface thereof isat least partially fusible at temperatures between 300 and 600Fahrenheit. In those embodiments of this invention in which the tape 22is a monolayer of solid colored plastic, it is not essential that tape22 include layer 27 of high melt adhesive, provided of course tape 22 bemade of'a plastic, which at least partially fuses in the temperaturerange 300 to 600 Fahrenheit and adhere to the substrate.

' Thus, used as herein, the terms high melt adhesive and adhesive layer27, are intended to include materials, generally considered to beadhesives which are activated by temperatures in the 300 to 600Fahrenheit range, as well as fusible materials, such as inks and/orplastic materials which develop adhesion to heated metal to which it isapplied. Thus, the adhesive can be a layer on the face of the tape or itcan be an integral part of the tape.

Thus, in accordance with this invention elongated prefinished metalstrip is converted in otherwise conventional equipment to completelyfinished butt welded tubing. The method is particularly useful inproviding butt-welded tubing having a wood grain finish.

I claim: I

1. The method of converting an elongated prefinished metal strip havinga longitudinal axis into a finished welded tube, comprising the steps:

a. advancing the strip in the direction of its longitudinal axis throughshaping means for imparting a substantially circular cross sectionthereto, thereby brining the edges of said strip to abutting position;

b. continuously welding together the edges of said strip thereby formingcontinuously tubing having a weld line, and thereby forming a heatedregion adjacent to and along both sides of the weld line; and applying acontinuous organic tape to said weld line and to a portion of saidheated region, said organic tape matching said prefinished metal stripin appearance and having a thickness between one-half and two mils andhaving a tube-contacting surface which is at least partially fusible andadherable at temperatures between 300 and 600 Fahrenheit, said applyingstep including initial contact between the tape and the tubing in thatportion of the heated region at which temperature is low enough to betolerated by the tape and yet is high enough to at least partially fusethe contacting surface so that it adheres to the tubing.

2. The method of claim 1 in which the tape includes a film of plasticselected from the group consisting of Mylar polyvinyl fluoride andpolyester.

3. The method of claim 1 in which the tape has printing on the underside thereof, and includes a high melt adhesive on the printed sidethereof said high melt adhesive being activated by temperatures between300 and 600 Fahrenheit.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. DatedAugust 24 1971 John E. Masters Inventor-(s) It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Abstract, line 4, cancel "matching".

Column 4, line 13, "brining"- should read bringing line 16,"continuously" should read continuous Signed and sealed this 14th day ofMarch 1972.

- (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents RM PO-105O 0-69) USCOMM-DC wave-ps9 \.l.5. GOVERNMENY PR NTNGOFFICE 9G9 O366'3]4

1. The method of converting an elongated prefinished metal strip havinga longitudinal axis into a finished welded tube, comprising the steps:a. advancing the strip in the direction of its longitudinal axis throughshaping means for imparting a substantially circular cross sectionthereto, thereby brining the edges of said strip to Abutting position;b. continuously welding together the edges of said strip thereby formingcontinuously tubing having a weld line, and thereby forming a heatedregion adjacent to and along both sides of the weld line; and applying acontinuous organic tape to said weld line and to a portion of saidheated region, said organic tape matching said prefinished metal stripin appearance and having a thickness between one-half and two mils andhaving a tubecontacting surface which is at least partially fusible andadherable at temperatures between 300* and 600* Fahrenheit, saidapplying step including initial contact between the tape and the tubingin that portion of the heated region at which temperature is low enoughto be tolerated by the tape and yet is high enough to at least partiallyfuse the contacting surface so that it adheres to the tubing.
 2. Themethod of claim 1 in which the tape includes a film of plastic selectedfrom the group consisting of Mylar polyvinyl fluoride and polyester. 3.The method of claim 1 in which the tape has printing on the under sidethereof, and includes a high melt adhesive on the printed side thereofsaid high melt adhesive being activated by temperatures between 300* and600* Fahrenheit.